U.S. patent number 4,383,586 [Application Number 06/265,089] was granted by the patent office on 1983-05-17 for adjustable linkage.
This patent grant is currently assigned to Setra Systems, Inc.. Invention is credited to Shih-Ying Lee.
United States Patent |
4,383,586 |
Lee |
May 17, 1983 |
Adjustable linkage
Abstract
Mechanical linkage comprising two pairs of flexure elements
constrains the motion of a reference member to be along a reference
axis even in the presence of applied moments. The linkage includes
a pair of V-shaped flexure elements coupled at their vertex ends to
the reference member at points along the reference axis. One of
these flexure elements is coupled at its distal ends to a support
member fixed with respect to the reference axis. The other of the
V-shaped flexure elements is coupled at its distal ends to one of a
pair of elongated flexure elements at a point between its two ends.
The pair of elongated flexure elements are affixed at one end to
the support member and at their other end are adjustably coupled to
the support member. This arrangement permits "fine tuning" of the
reference axis so that the linkage exhibits the desired high
resistance to moments applied to the reference member.
Inventors: |
Lee; Shih-Ying (Lincoln,
MA) |
Assignee: |
Setra Systems, Inc. (Natick,
MA)
|
Family
ID: |
23008935 |
Appl.
No.: |
06/265,089 |
Filed: |
May 19, 1981 |
Current U.S.
Class: |
177/229;
177/255 |
Current CPC
Class: |
B23Q
1/36 (20130101); G01G 21/244 (20130101); F16H
21/04 (20130101) |
Current International
Class: |
B23Q
1/36 (20060101); B23Q 1/26 (20060101); F16H
21/04 (20060101); F16H 21/00 (20060101); G01G
21/24 (20060101); G01G 21/00 (20060101); G01G
003/08 (); G01G 021/24 (); E04G 003/00 () |
Field of
Search: |
;177/229,255
;248/274 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Miller, Jr.; George H.
Attorney, Agent or Firm: Kenway & Jenney
Claims
I claim:
1. Linkage for constraining motion of a reference member to be
parallel to a first reference axis, said first reference axis being
fixed with respect to a support member, comprising:
first and second elongated flexure members, said first and second
flexure members having a flexure near one end, said one end fixedly
coupled to said support member, said first and second flexure
members having their other ends adjustably coupled to said support
member, whereby said other ends may be selectively positioned in
the direction of said first reference axis,
first and second V-shaped flexure elements, each flexure element
having a vertex end portion and flexure portions extending
therefrom and terminating at first and second distal end
portions,
wherein said vertex end portions of said first and second V-shaped
flexure elements are fixedly coupled to said reference member at a
respective one of points B and C, said points B and C being
separated by distance X in the direction of said first reference
axis,
wherein the first and second distal ends of said first V-shaped
element are fixedly coupled to a respective one of said elongated
flexure elements at a respective one of coupling points A and D,
said points A and D being between said flexures at said one ends
and said other ends of said elongated flexure elements, and lying
along a second reference axis nominally perpendicular to said first
reference axis,
wherein the first and second distal ends of said second V-shaped
element are fixedly coupled to said support member at a respective
one of points E and F, said points E and F lying on a third
reference axis, said third reference axis perpendicular to said
first reference axis,
wherein said adjustable couplings are adjustable whereby the
distance between points A and F in the direction of said first
reference axis equals the distance between points D and E in the
direction of said first reference axis and said second reference
axis is parallel to said third reference axis and offset therefrom
by distance X in the direction of said first reference axis.
2. A linkage according to claim 1 wherein said flexure members and
said flexure elements include beams and hinges.
3. A linkage according to claim 1 wherein said flexure members and
flexure elements have distributed flexures.
4. A linkage according to claim 1 wherein the distance AB between
points A and B equals the distance DB between points D and B, and
the distance FC between points F and C equals the distance EC
between points E and C.
5. A linkage according to claim 4 wherein AB=FC.
Description
REFERENCE TO RELATED APPLICATION
The subject matter of this application is related to that of U.S.
patent application Ser. No. 265,088, Weighing System, filed on even
date herewith.
BACKGROUND OF THE INVENTION
The present invention is in the field of mechanical linkages, and
more particularly, relates to linkages for controlling motion of an
element to be along a reference axis.
Linkages for constraining motion of an element to be along a
reference axis are particularly useful in weighing systems, or
scales, where it is desired to sense the weight of an object. Such
systems require transfer of the gravitational force of the object,
for example, in a weighing pan, to a force sensor without the
introduction of error components due to friction and other sources.
Typically, off-center loading of the object in the pan leads to
moments being applied to the various elements linking the pan to
the sensor. These moments, in turn, generally produce additional
forces along the sensitive axes which may cause measurement
error.
In the prior art, it is known to reduce the effect of off-center
loading by coupling the weighing pan to the sensor by a
parallelogram linkage. In one form, a pair of V-shaped flexure (or
hinged) elements, each having a vertex portion and a pair of distal
end portions, is configured with the distal end portions being
affixed to a support member or casing, so that the V-shaped members
lie in parallel planes. A connecting link is fastened between the
vertex portions of the flexure elements. With this configuration,
in order to precisely constrain the motion of the reference member
coupled to the link to a motion along that reference axis, the
V-shaped elements must be precisely positioned with respect to the
support member in order to achieve the desired parallelism. With
this configuration, the motion of the reference member is highly
resistant to applied moment. However, as a practical matter, the
precise positioning of the V-shaped elements requires critical
alignment of those elements during fastening the distal ends of
those elements to the support member.
It is an object of the present invention to provide an improved
linkage for constraining the motion of an element to motion along a
reference axis.
SUMMARY OF THE INVENTION
Briefly, the present invention is directed to a linkage for
constraining motion of a reference member to be along a first
reference axis. The linkage includes a vernier control assembly to
permit "fine tuning," or adjustment of the linkage to provide a
precisely controlled motion of the reference member along the
desired axis, even in the presences of applied moments. The linkage
includes a pair of elongated flexure members, each having one end
affixed to a support member and the other end adjustably coupled to
the support member so that the latter end may be selectively
positioned in the direction of the first reference axis. The
elongated flexure members are affixed to support member at points
lying along a second reference axis which is perpendicular to the
first reference axis.
The linkage further includes two V-shaped flexure elements, each
having a vertex end portion and a pair of distal end portions. The
vertex end portions of the flexure elements are coupled to the
reference member at points offset by distance X in the direction of
the first reference axis. The distal end portions of one of the
V-shaped flexure elements is coupled to the support member at
points lying along a third reference axis, where the third
reference axis is parallel to the second reference axis. The distal
end portions of the other V-shaped flexure element are coupled to
an associated one of the elongated flexure members at a point
between its two ends.
With this configuration, the parallelism of the two V-shaped
flexure elements may be precisely aligned by adjustment of the
adjustable coupling at the ends of one or both of the elongated
flexure members. When so adjusted, the linkage is highly resistant
to moments applied to the reference member.
BRIEF DESCRIPTION OF THE DRAWINGS
The foregoing and other objects of this invention, the various
features thereof, as well as the invention itself, may be more
fully understood from the following description, when read together
with the accompanying drawings in which the FIGURE shows an
exemplary embodiment of the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENT
FIG. 1 shows an exemplary embodiment of the present invention. In
this form, a linkage 110 is shown which is adapted for constraining
the motion of a reference member 112 to be along a first reference
axis 116, where that first reference axis 116 is fixed with respect
to a support member 220. The linkage 110 includes a pair of
elongated flexure members 124 and 126. The flexure members 124 and
126, as shown, are beams with flexures indicated by reference
designations 125 and 127, respectively, positioned at one end. The
flexures 125 and 127 at the ends of each of members 124 and 126 are
coupled by a respective one of beam portions 124a and 126a to the
support member 220.
The other end of each of members 124 and 126 is coupled by means of
an adjustable coupling assembly to the support member 220. The
adjustable coupling assembly for member 124 includes a screw 130
near the free end of member 124, and an associated threaded hole in
an extension portion 132 of support member 220. The motion of that
end of flexure 124 is opposed by a spring 134. With this
configuration, the screw 130 may be turned to adjustably position
the free end of flexure member 124 in the direction of axis
116.
In a similar manner, the adjustable coupling assembly for member
126 includes a screw 131 near the free end of member 126, an
associated threaded hole in extension portion 132, and a spring
135. Screw 131 may be turned to adjustably position the free end of
flexure member 126 in the direction of axis 116.
The linkage 110 further includes two V-shaped flexure elements 136
and 138, with each of elements 136 and 138 including a vertex end
(including a flexure, or hinge) and two distal end portions (each
including a flexure, or hinge). The vertex portions of the flexure
elements 136 and 138 are coupled (by extension beam portions 136a
and 138a beyond the vertex flexure) to the ends of the reference
member 112, at points B and C, respectively, where points B and C
are separated by distance X in the direction of axis 116.
The first and second distal ends of element 136 are connected at
coupling points A and D, respectively, by way of extension beam
portions 136b and 136c, respectively (beyond the distal end
flexures) and a respective one of spacer elements 142 and 143 one
of flexure elements 124 and 126 between the flexures and free ends
of those members. Points A and D lie along axis 140 which is
nominally perpendicular to axis 116. In the preferred form, points
A and D are on the order of one-tenth of the distance from the
flexure to the free end of the respective elements 124 and 126.
The first and second distal end portions of the V-shaped element
138 are coupled to the support member 220 (by extension beam
portions 138b and 138c, respectively, beyond the distal end
flexures) with their respective flexures positioned at points E and
F, respectively. Points E and F lie on a third reference axis 144
which is perpendicular to axis 116.
When axis 140 is parallel to axis 144, and separated therefrom by
distance X in the direction of axis 116, the motion of reference
member 112 is constrained to be substantially along the axis 116.
Moreover, the member 112 is substantially resistant to moments
about axis 116.
The linkage 110 is particularly easy to adjust so that axes 140 and
144 are parallel. Generally, the screws 130 and 131 may be
adjustably positioned to achieve a "fine tuning" or precise control
of this parallelism. The position of points A and D along flexure
elements 124 and 126 may be selected to provide a desired vernier
control of the trueness of this parallelism. In the preferred form,
points A and D are one-tenth the distance from the respective ones
of flexures 125 and 127 to the free ends of the elements 124 and
126, respectively.
In the illustrated form of the invention, the distance between
points A and B equals the distance between points D and B, and the
distance between points F and C equals the distance between points
E and C. These relationships permit the maximum range of motion of
member 112 along axis 116, although other relationships may also be
used.
In the illustrated embodiment, elements 124, 126, 136 and 138 are
relatively rigid beams with flexures at discrete locations. In
alternate embodiments, these elements may be replaced with elements
having a distributed flexure, for example, spring steel.
The invention may be embodied in other specific forms without
departing from the spirit or essential characteristics thereof. The
present embodiments are therefore to be considered in all respects
as illustrative and not restrictive, the scope of the invention
being indicated by the appended claims rather than by the foregoing
description, and all changes which come within the meaning and
range of equivalency of the claims are therefore intended to be
embraced therein.
* * * * *